Bleaching of synthetic fibers,alone or mixed with natural and/or artificial cellulose fibers



5 Claims. c1. ss ABSTRACT OF THE DISCLOSURE A method is provided for the bleaching of synthetic textile fibers alone or in admixture with natural and/or artificial cellulose fibers. The fibers are first pre-soaked in an aqueous solution of a bleaching agent selected from the group consisting of trichlorocyanuric acid, a mixture of trichlorocyanuric acid and cyanuric acid, and a mixture of alkali metal or alkaline earth metal hypochlorite and cyanuric acid. The pre-soaked material is then subjected to a squeezing operation at ambient temperature until the solution takeup amounts to about 50% to 120% of the weight of the said material. Then, as the bleaching step-proper, the resultant impregnated-and-squeezed material is maintained at a temperature between the squezing temperature and 100 C. for a period ranging from about 1 minute to several hours.

The present invention is concerned with the bleaching of synthetic fibers, alone or in admixture with natural and/ or artificial cellulose fibers. It also relates to a novel bleaching bath composition useful in effecting bleaching of the said fibers.

Of the various bleaching agents which have, from time to time, been employed in the synthetic textile industry, sodium chlorite in aqueous solution appears to lead to particularly interesting results. However, the use of aqueous solutions of sodium chlorite is bound up with serious drawbacks because of the necessity of operating at pH values of about 3 and, in many cases, at comparatively high temperatures, in order to obtain satisfactory whiteness of the bleached material. These operating conditions result in the formation of chlorine dioxide, a gas which is toxic to men and corrosive to equipment-and this is very detrimental, particularly where such bleaching technique is applied to modern continuous or semi-continuous processes.

A primary object of the present invention is the embodiment of a commercially feasible bleaching process for the said fibers, which process is free of the aforesaid drawbacks of the aforedescribed prior process.

The said object is realized by the present invention according to which, briefly stated, the aforementioned fibers or mixtures of fibers are bleached by means of a chlorinating agent consisting of (a) at least one N-chlorinated derivative of cyanuric acid;

(b) at least one N-chlorinated derivative of cyanuric acid in admixture with cyanuric acid, i.e. unchlorinated cyanuric acid;

(c) at least one alkali metal hypochlorite or alkaline earth metal hypochlorite, in admixture with cyanuric acid.

The chlorinating agent (a), (b) or (c) is employed in aqueous solution.

The bleaching operation, according to the invention, comprises a preliminary impregnation and a subsequent SEARS? Patented Nov. 26, 1968 bleaching step proper. The preliminary impregnation is effected by soaking by the wrapping-up technique or by direct immersion of the fibers or fibrous material in the aforesaid chlorinating agent-containing aqueous solution at a temperature in the range of from about 10 C. to about 30 C., followed by a conventional squeezing or wringing operation to remove excess bleaching solution therefrom. Preferred take-up according to the invention ranges from about 50% to about 120% of the dry weight of the material to be bleached.

The bleaching step proper follows the preliminary (soaking) operation, as just described, and is carried out at a temperature ranging from room temperature, about 20 to 30 C., to about 100 C. for a period ranging from one as short as one minute to one as long as several hours.

It is an important feature of the present process that the entire bleaching operation-pre-soaking, expressing and bleaching step properis carried out at a pH between 5 and 8, this being achieved by the addition, if necessary, to the aqueous solution of bleaching agent of salt of slightly alkaline reaction, such as sodium carbonate, sodium bicarbonate or sodium phosphate or by the addition of dilute inorganic acid, such as dilute hydrochloric or dilute sulfuric acid, or a dilute organic acid, such as dilute acetic acid.

The maintenance of the aforesaid pH (5 to 8) is essential to the realization of the desired results with the bleaching agents according to this invention. This will be clear from a consideration of the following test data established with bleaching baths of different compositions according to the invention and with a control bath based on sodium hypochlorite as bleaching agent, as a function of pH:

Bath I Bath II Bath III pH values B A B A B s s s ewew eaeeaaa Columns A and B set forth respectively the percentages of available chlorine in the tested baths after 10 and 20 minutes heating at C. The three baths I, II and III have an initial content of available chlorine of 5.5 to 6.0 grams per liter.

Bath I is constituted by an aqueous solution of 6.0 grams per liter of trichlorocyanuric acid, 1.7 grams per liter of cyanuric acid and 2.1 grams per liter of sodium carbonate (or 3.3 grams per liter of sodium bicarbonate). The initial pH of the bath is 5.75 to 5.8 and this is varied in both directions, during the tests, by careful additon of sodium bicarbonate or sodium carbonate, on the one hand, or dilute sulfuric acid, hydrochloric acid or acetic acid, on the other hand.

Bath II is prepared by admixing 130 milliliters of an aqueous solution of sodium hypochlorite at 16 chlorometric (53 grams per liter of available chlorine) with 200 milliliters of an aqueous solution containing 5.75 grams of cyanuric acid and 13.5 grams of sodium hydroxide. 29 milliliters of the resultant solution are diluted to 100 milliliters with water. The initial pH of this bath, which contains 6.1 grams per liter of available chlorine, is 12.1. In the tests, this pH value is varied by adding increasing amounts of dilute aqueous acid.

Control bath III is composed of an aqueous solution of sodium hypochlorite of 3235 chlorometric (96 grams per liter of available chlorine). The initial pH of 11.5 of this solution is lowered during the testing by adding increased amounts of dilute hydrochloric or sulfuric acid.

The results set forth in the preceding table make evident the fact that the mixture of trichlorocyanuric acid and cyanuric acid (bath 1) and the mixture of sodium hypochlorite and cyanuric acid (bath II), according to the invention, have a similar behavior in these tests which show the stability of the tested solutions.

The stability of baths I and II, which is very high in the pH range of 5 to 8 and beyond pH 12, is greatly decreased between pH 9 and 12, with a minimum value at between pH 11.0 and 11.5. On the other hand, the hypochlorite solutions (III) prove very unstable at pHs comprised between 6 and 8, maximum instability appearing in the vicinity of neutrality.

However, it is in the vicinity of neutrality that the highest bleaching rates appear, so that it is a desideratum to be able to operate in this pH region with bleaching materials which are stable under the operating conditions, such as stability being imperious in other respects to avoid any fiber deterioration.

In sharp contrast to bleaching baths based on alkali metal or alkaline earth metal hypochlorites without cyanuric acid, the bleaching bath compositions according to the present invention offer such advantages, i.e. maximum stability in the neutral pH region whereby the possibility of operating in this region is assured. Moreover, the bath compositions of the invention make it easier to carry out the per se essentially conventional dechlorinating operation which follows the bleaching operation, since the said compositions allow consumption of almost all the active chlorine.

By synthetic fibers in the context of the present specification, there are meant the various man-made fibers such for example as acrylic fiber (at least 85% by weight polyacrylonitrile), poly(acrylonitrile) co vinyl acetate, polyacrylonitrile, nytril fiber (at least 85% by weight poly [vinylidene dinitrile]), polypropylene fiber, poly(vinylidene chloride) fiber, polyurethane (at least 85%) fibers, poly(vinyl chloride) fibers, etc. By natural cellulose is primarily meant cotton. By artificial cellulose fibers are meant cellulose acetate fibers, cellulose triacetate fibers, regenerated cellulose (rayon or viscose) fibers, etc.

The materials being bleached may be in various forms, e.g. flutfs, fabrics, ribbons, ropes, etc.

The bleaching agents compositions made up of a mixture of trichlorocyanuric acid (which, more precisely, is N-trichlorocyanuric acid) and cyanuric acid (unchlorinated) generally contain these ingredients in a 2 to 1 molar ratio.

The following examples set forth presently preferred exemplary embodiments of the invention.

EXAMPLE 1 A bleaching bath is prepared as follows: A mixture of 9.3 grams per liter of trichlorocyanuric acid and 2.6 grams per liter of cyanuric acid is prepared by first homogeneously mixing the said two ingredients in the dry state in the molar proportion of 2:1. The mixture is then dissolved in cold water in an amount of 11.9 grams per 4 liter of water, in the presence in the water of 5.05 grams per liter of sodium carbonate. The pH of the bath is 5.85.

A polyacrylic fiber fabric (made on the basis of fibers commercially available as Crylor) is first soaked in the said bath at a temperature of about 20 C. The thusimpregnated fabric is then squeezed to an uptake of 100% of solution (100% wet) and entered into a steaming apparatus, advantageously a so-called J box conventionally used in bleaching with chlorine, wherein it is held for period of 5 minutes at 100 C. whereupon the bleaching is complete.

The thus-bleached fabric is then entered into a dechlorinating bath, heated to C. and containing 8 grams per liter of sodium bisulfite and 1 milliliter per liter of 2P-21 B. hydrochloric acid. After squeezing the thus-soaked fabric, it is wrapped around a roller and the ensuing dechlorination reactions allowed to proceed for a period of one hour, whereupon the dechlorinated fabric is subjected to washing with water in a conventional washer to remove bleaching and dechlorinating materials as well as impurities still present therein.

The fabrics thus bleached present a satisfactorily improved whiteness. If desired, the fabrics can be aftertrcated with optical bluing agents.

EXAMPLE 2 One liter of bleaching bath is prepared by making a slurry with 9.1 grams per liter of cyanuric acid in 100 milliliters of water and adding to the resultant pasty product 100 milliliters of an aqueous solution of 20% strength sodium hydroxide, followed by 125 milliliters of aqueous solution grams per liter) of sodium hypochlorite. The pH at this stage is 12.2 and this is lowered to 6.3-6.4 by adding, while stir-ring and cooling, the required amount of 32% sulfuric acid, after which the volume of the solution is made up to one liter by the addition of water. The thus-obtained solution, which contains 10 grams per liter of available chlorine, is used to impregnate a rope of polyacrylic fibers (Crylor) at ambient temperature. After squeezing to an about 100% wet state, the rope is heated to 100 C. for 2 minutes, and then dechlorinated with sodium bisulfite or hydrogen peroxide, rinsed and dried.

The product is well bleached.

EXAMPLE 3 A mixed fabric (70% by weight of polyester (Dacron) fibers and 30% by weight of cotton fibers) is pre-soaked in a 1000 liter bath, pH 6, containing 8 grams per liter of available chlorine, and being constituted by 8.8 kilograms of trichlorocyanuric acid, 2.7 kilograms of sodium carbonate and a sufficient amount of water to make up the indicated volume.

The thus-soaked fabric is squeezed down to an about 100% wet state, and is then placed in a I-shaped steaming apparatus (1 box) wherein it is retained for a period of 5 minutes at 100 C., after which it is washed in a multi-vat washer, the first vat of which is used for rins ing with water and the second for dechlorinating by means of an alkaline solution of hydrogen peroxide. Additional vats, which may be three in number, are used for hot and cold rinsing with water.

The fabric thus treated is of satisfactory whiteness and presents perfect hydrophility. No deterioration of fibers is noted. Furthermore, as a result of the afore-described treatment, it becomes unnecessary to remove spinning dressings and gumming.

EXAMPLE 4 A bleaching bath constituted by sodium hypochlorite and cyanuric acid in solution in water, having a pH of 5.9 and containing 5.4 grams per liter of available chlorine, is made up according to the procedure of Example 2 mutatis mutandis.

A fabric of polyvinyl chloride is impregnated to wet with the aforesaid solution, after which the bleaching step proper is carried out by the per se conventional wrapping up technique for minutes at 60 C.

The thus-bleached fabric is then rinsed in a washer with a dechlorinating solution containing 1 gram per liter of sodium bisulfite at 50 C., and is thereupon washed with water and dried.

The fabric presents a very good whiteness; no deterioration of fibers is noticeable.

EXAMPLE 5 A mixed fabric made of 2 parts by weight of polyester (Dacron) fibers and 1 part by weight of viscose fibers is impregnated to 102% wet With an aqueous solution of trichlorocyanuric acid and cyanuric acid of pH 7.2 with an available chlorine content of 1.8 grams per liter, followed by bleaching in a continuous operation. After steaming at C. for 2 minutes, dechlorination is carried out in continuous operation with an aqueous solution of 0.8 gram per liter of sodium bisulfite at 20 C. The average degree of polymerization of the staple fiber remains substantially unaltered during the treatment.

EXAMPLE 6 A woven mixed fabric (2 parts by weight of polyester [Dacron] fiber and 1 part by weight of viscose fibers) is impregnated to wet with an aqueous bleaching solution of trichlorocyanuric acid and cyanuric acid of pH 6.8 containing 2.5 grams pers liter of available chlorine. The impregnated fabric is wrapped up cold and, after 2 hours contact, is subjected to dechlorinating in a washer by means of an aqueous solution containing 1 gram per liter of sodium bisulfite. After washing and drying, the fabric presents a good whiteness.

Having thus disclosed the invention, what is claimed s 1. A method of bleaching synthetic textile fibers, alone or in admixture with natural and/or artificial cellulose fibers, which comprises first pre-soaking the material being bleached with an aqueous solution of a bleaching agent selected from the group consisting of trichlorocyanuric acid, a mixture of trichlorocyanuric acid and cyanuric acid, and a mixture of alkali metal or alkaline earth metal hypochlorite and cyanuric acid, then subjecting the pre-soaked material to a squeezing operation at ambient temperature until the solution take-up amounts to about 50% to of the weight of the said material, and maintaining the resultant impregnated-and-squeezed mate rial at a temperature between the squeezing temperature and 100 C. for a period ranging from about 1 minute to several hours, the recited operations being carried out at a pH in the range of from 5 to 8.

2. A method according to claim 1, wherein the resultant bleached material is subjected to dechlorination, followed by washing with water and drying.

3. A method according to claim 1, wherein the bleaching agent is trichlorocyanuric acid.

4. The method according to claim 1, wherein thebleaching agent is a mixture of trichlorocyanuric acid and cyanuric acid.

5. The method according to claim 1, wherein the bleaching agent is a mixture of alkali metal or alkaline earth metal hypochlorite and cyanuric acid.

References Cited UNITED STATES PATENTS 3,213,029 10/1965 Muchow et al 252-99 MAYER WEINBLATT, Primary Examiner. 

